Self cleaning strainer

ABSTRACT

A backwash strainer having a generally cylindrical filter element made up of a stack of spaced rings that are triangular in cross section, with the bases of said triangular rings disposed in a cylindrical surface. A hollow backwash arm has an open slot disposed on the inside of the cylindrical surface which operates at a predetermined distance from said element. The incoming water in said strainer flows from the inlet up through the straining element to the outlet. The backwash arm receives water from around the straining element, which flows through the element into the backwash slot and out with the debris accumulated on said strainer. Since the debris is supported on the flat interior of the rings, water flowing back into the arm into the slot in the hollow backwash arm forces trash and other debris from the rings down to the backwash water outlet. Water flowing through the clearance between the bars as used, helps flush the debris off the inside of the filter element.

FIELD OF INVENTION

Our invention relates to improvements in automatic backwashing typestrainers or filters and, more particularly, to strainers for a fluidmedia which includes fibrous or other forms of debris which tend to mat,staple and clog the strainer element.

REFERENCE TO PRIOR ART

Fluid strainers have been employed for many years in which accumulatedsolids or sedimentation strained from the fluid is collected on thescreening media and thereafter removed from the screening media by meansof backwashing in which a portion of the fluid being strained is causedto flow in a reverse direction to clean the strainer. More recently ithas been recognized that the backwashing liquid may be supplied from anexternal source and at a pressure above the pressure of the fluid in thestrainer. Exemplary of this is U.S. Pat. No. 3,074,560.

It has also been known to provide a scraping shoe which advances overthe surface of a straining member and removes surface deposits which arethen accumulated and immediately backwashed through a discharge.Exemplary of such strainers in U.S. Pat. No. 2,275,958.

It is also known that a plurality of wire brushes may be employed whichengage the filter plate and remove the sediment therefrom. Exemplary ofsuch strainers is U.S. Pat. No. 3,017,029. Screens per se have been madeof wire, triangular in cross section, and have been as shown in U.S.Pat. No. 4,348,284 wherein a rod is wound in the form of a helixproviding a slot of continuously increasing width.

While all of the above designs have useful applications, problems arisewhere fibrous or other debris which tends to mat is carried in the fluidto be strained. The fibrous debris tends to mat and entangle itself onthe straining media, thereby making removal by the conventional means ofreverse flushing very difficult and often virtually impossible.

One such patent which recognizes the problems of fibrous debris adheringto the strainer element is U.S. Pat. No. 3,392,839. That patent teachesthe use of a fine mesh strainer element in combination with otherelements in the form of honeycomb grids, the action of which preventsexcessive entanglement and build up of fibers in and on the fine meshelement. The honeycomb grids may conveniently be made up of an assemblyof metal strips in which the ratio between the length and cross sectionof the apertures is such as to shield the intermediate fine mesh screenfrom excessive contact with the fibrous debris.

U.S. Pat. No. 3,357,566 shows a backwash filter having an inlet, a firstoutlet and a backwash outlet with a backwash arm having rubber edgesdefining a slot that engages the inside of the filter basket. The filterelement basket is made up of vertically spaced rods.

U.S. Pat. No. 4,135,820 utilizes a strainer element made of a pluralityof stacked spaced concentric rings, rectangular in cross-section, withperpendicularly disposed bars, spaced both inside and outside of thebasket. The bars, together with the top and bottom ring define a seriesof compartments along the strainer element formed by the protrudingsurfaces of engagement with the rotating backwash supply arms. Thesecompartments collect the debris and where the debris extends into anadjacent compartment, a shearing means causes shearing of the debrisinto section for eventual removal. This design of strainer element iscomplex and not simple and can result in undesirable pressures built upinside the strainer element.

SUMMARY OF THE INVENTION

Our design is specifically intended for improvements in strainers,straining media and backwash device on which fibrous or other debristends to plug or clog the media making removal by conventional meansvirtually impossible. We further provide a screen and backwash designwhich is more effective than existing means and reduces the loss ofvaluable fluids.

We provide an automatic backwashing strainer having a fixed strainingmedia and a rotating, backwashing device. The backwashing device of therotary type develops high velocity liquid for backwashing. We furtheremploy a new design for the straining media in which the straining mediaincreases in size in the direction of flow so as to provide a smooth,flat surface to trap debris and reduce the possibility of retainingparticles smaller than the screen opening.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal cross-sectional view of a strainer according tothe invention.

FIG. 2 is a cross-sectional view taken on line 2--2 of FIG. 1 with thestrainer element removed.

FIG. 3 is an isometric view of the strainer element according to theinvention.

FIG. 4 is a partial enlarged longitudinal view of the strainer elementshown in FIG. 3.

FIG. 5 is a partial side view of the strainer element.

FIG. 6 is a cross-sectional view of the strainer element taken on line6--6 of FIG. 5.

FIG. 7 is a partial view from the inside of the strainer element lookingout.

FIG. 8 is an enlarged partial cross-sectional view taken on line 2--2 ofFIG. 1.

FIG. 9 is an isometric view of the embodiment of the invention shown inFIGS. 9 through 14.

FIG. 10 is an enlarged partial cross sectional view taken on line 9--9of FIG. 11.

FIG. 11 is a cross sectional view of the strainer shown in theembodiment of the invention of FIGS. 9 through 14.

FIG. 12 is a partial longitudinal cross sectional view of the embodimentof the invention shown in FIGS. 9 through 14.

FIG. 13 is a side view of the strainer element shown in the embodimentof the invention of FIGS. 9 through 14.

FIG. 14 is a partial enlarged cross sectional view similar to theembodiment of the invention shown in FIG. 8.

DETAILED DESCRIPTION OF THE DRAWING

Now with more particular reference to the drawings, the strainer 10disclosed herein is made up of a body 12, which may be a generallycylindrical body, having a closed top 44 and a closed bottom 46. Thebody 12 has a hollow, generally cylindrical partition 43 which alsofunctions as a support for the strainer element 18. Partition 43 isdisposed concentrically in the lower part of the body 12 and rests onthe closed bottom 46. Inlet tube 14 is connected through an opening 48in the side of the partition 43. Outlet 16 extends through the outerwall of the body 12.

Strainer element 18 comprises a hollow cylindrical configuration and isconcentrically disposed inside the body 12 with a space 88 between theinner walls of the body 12 and the outer surface of the strainer element18 around the cylindrical partition. The strainer element 18 has a firstring 51 on its upper end that fits into ring 61 on the body and a secondring 52 on its lower end which rests on ring 60 on body 12.

Closed top 44 forms a closure for the upper end of the strainer element18. The strainer element 18 rests on the ring 60 which is welded to theupper end of the cylindrical partition 43. Support ring 60 is welded toand is therefore is an integral part of the partition 43. Ring 60 ismachined concentric with ring 61 to guide the strainer element 18 andsupport it concentric with the hollow shaft 50, offering a smooth,efficient, cleaning operation of the removal of the dirt from thestrainer and extending the life of hollow bearing 76. The motor andspeed reducer unit 38 is supported on the top 44 and has a gearreduction unit or other suitable drive indicated at 62, operativelyconnected to the hollow shaft 50 and extending through a packing 64 intothe interior of the strainer element 18.

The hollow backwash shaft 50 may be square or round in cross-section andhave a slot 66, which communicates with the inside of the backwash arm32. The backwash arm 32 is made up of two spaced plates 68 and 70 whichdefines a slot 66, which terminates in open ends 54 and 56 defining slot66.

The lower end of hollow backwash shaft 50 is received in the hollowbearing 76, which is supported on backwash pipe 42 and communicates withthe backwash pipe 42. The backwash pipe 42 discharges through thebackwash outlet 78, which may be connected to a suitable drain. A bar58, which may be made of brass, is supported on plate 68. Bar 58 isgenerally rectangular in cross-section and terminates in a cornerportion 80, which moves in closed spaced relation to the inside surfaceof the strainer element 18. Since the inside of the slot 66 is exposedto atmospheric pressure and the liquid in the space 88 is underpressure, liquid will tend to flow from space 88 back through thestrainer element 18 to the inside of slot 66.

The strainer basket, shown in FIGS. 3 through 8, is made of a pluralityof spaced concentric rings 20, triangular in cross section, stacked witha space of, for example, 0.003 to 0.025 inches between them. Spacedvertical rods 30 hold rings 20 in position. Plate-like end rings 51 and52 are attached to vertical rods 30.

As an alternate, the strainer element 18 can be made with a plurality ofstraight bars 120, triangular in cross section, disposed vertically inclosely spaced relation defining a hollow cylinder. Rings 130, in theform of circumferential hoops, may be disposed horizontally as shown inFIGS. 9 through 14. Rings 130 hold bars 120. The inside surface (base122) of bars 120 define a hollow cylinder. The rings are triangular incross section and have base 122 and sides 124 and 126. The adjacentsides 124 and 126 meet at apex 128 remote from the base 122. The rings130 are disposed generally perpendicular to the rings 120 and attachedto the rings 120 on the outside thereof, holding the bars 120 in spacedrelation to one another. The space between the bars 120 is defined asthe screen opening 119, which can vary in size from 0.003 inches to0.250 inches and larger. Supports 151 and 152 are fixed to the ends ofbars 120. The vertical bars can be spaced at any suitable distancedepending on the material being handled, for example, the vertical barscan be spaced 0.003 inches to 0.250 inches from one another. The bases122, of the generally triangular cross sections of the bars 120, aredisposed with their bases 122 facing inward, and apexes facing outward,each disposed in the surface of a cylinder defining an inside surface ofthe strainer element 118. The apex 128 of each of the generallytriangular cross sections of the rings 120 may be welded to the supportbars 130.

The screen may be made by winding the triangular cross section wireforming rings 20 spirally around a form or the array of support rodsforming a helix. The helix may be split to form rings and the rings maybe welded to support rods to form the configuration as shown in FIG. 3.The rings are then rewelded if desired.

The rotating hollow shaft 50 has axle means supporting the hollowbackwash arm 32 on the strainer body 12 for rotation about a centralaxis of the strainer element 18. The hollow backwash arm 32 extendsoutwardly from the hollow shaft 50. The backwash pipe 42 has a centralaxis 77 and terminates in close spaced relation to the inner peripheryof the strainer element 18. The outer ends of the plates 68 and 70terminate in close spaced relation to the inner periphery of thestrainer element 18. The clearance A at space 82 may be on the order of1/32 of an inch. Plate 70 has a clearance B of 3/8" to 1", depending onsize, between it and the inner periphery of strainer element 18. The bar58 is supported on bracket 84 and fixed to plate 68 by means of asuitable fastener. Bar 58 has a corner portion 80 with a very smallclearance between the bar 58 and the strainer element 18.

In operation, when a supply of water to be filtered is connected to theinlet tube 14 flows through the strainer element 18 and dischargesthrough the outlet 16 the water, filters out through the element 18 intothe space 88 between the strainer element 18 and the body 12, debrisfrom the water is left on the inside of rings 20. As the backwash arm 32rotates, filtered water from space 88, flows back through the strainerelement 18 into the slot 66 between plates 68 and 70 and carry with itthe debris that has accumulated on the inner surfaces of the rings 20 orbars 120. Since the spaces between the sides 24 and 26 of adjacent ringsincrease in size in an outward direction and become larger than thespace that is small enough to pass between the bases 20, any materialbetween the rings will tend to be washed away with the filtered waterand will not lodge between the bars. Bar 58 will break loose any debristhat may lodge between rings 20.

The foregoing specification sets forth the invention in its preferred,practical forms but the structure shown is capable of modificationwithin a range of equivalents without departing from the invention whichis to be understood is broadly novel as is commensurate with theappended claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A backwash strainercomprising a cylindrical body,a cylindrical strainer element in saidbody, an annular space between said cylindrical body and saidcylindrical strainer element, an inlet in said body to said strainerelement, an outlet from said annular space, said element comprising aplurality of substantially parallel, equally spaced bars, said parallelbars defining a cylindrical surface with spaced slots between saidparallel bars, support means attached to said bars holding said bars inspaced relation to one another, a hollow backwash arm having an axiallyextending slot defined by two spaced members having ends, said backwasharm being movable about a central axis moving said ends of said backwasharm in close spaced proximity relation to said cylindrical surfaceproviding a space for backwash water to flow between said ends of saidbackwash arm and said cylindrical surface for washing foreign materialfrom said inside surface into said backwash arm to said dischargeoutlet.
 2. The backwash strainer recited in claim 1 wherein,said barscomprising a plurality of annular rings, said rings being generallytriangular in cross-section, said generally triangular cross-sections ofsaid rings having a relatively flat base and sides, said sides of eachsaid ring meeting at an apex remote from said base, said support meanscomprising a plurality of supports disposed generally perpendicular tosaid rings and attached to said rings, holding said rings in spacedconcentric relation to one another, said bases of each said ring beingdisposed generally in said cylindrical surface of said cylindricalstrainer element.
 3. The strainer recited in claim 1 whereinsaid end ofone of said two spaced members has a second bar attached thereto andspaced from said cylindrical surface to engage debris on saidcylindrical surface.
 4. The strainer recited in claim 2 wherein saidrings are parts of a spiral rod,said triangular shaped rings providespaces for only two point particle retention that reduces thepossibility of debris remaining on said strainer element after acleaning operation, whereby the slotted space design reduces thepossibility of retaining particles smaller than the screen opening,preventing premature clogging of said strainer element.
 5. The strainerrecited in claim 4 wherein said spiral rod is cut axially forming ringshaving ends and said ends are welded together.
 6. The strainer recitedin claim 3 wherein said strainer element is made up of a first end ringand a second end ring on its opposite end,said support bars holding saidend rings in spaced relation to one another, said rings providing spacessufficiently small to strain debris of predetermined sizes from aliquid, said triangular cross-sections of said rings having a base andtwo sides adjacent said base, said sides adjacent said base terminatingin an apex, said apex of each said ring being fixed to said supportbars, said bases of said triangular shaped circular/annular rings beingdisposed in a cylindrical surface.
 7. The strainer recited in claim 2wherein said strainer has motor means supported on it,said motor meansbeing fixed to said hollow shaft.
 8. The strainer recited in claim 7wherein said hollow shaft is connected to said backwash arm.
 9. Thestrainer recited in claim 8 wherein said rings define a cylindricalsurface with axially spaced slots and,said backwash arm providespassages for filtered water to pass through said slot.
 10. The strainerrecited in claim 3 wherein said vertical bars are closely spaced to oneanother providing said inwardly facing cylindrical surface.
 11. Thestrainer recited in claim 3 wherein said rings are closely spaced fromone another providing said inwardly facing cylindrical surface.